effectively increasing the window's R value. Some of the low E coatings are also designed to reject
infrared energy from the sun, thus reducing air conditioning loads. Electrochromic window coatings in the
development stage offer dynamic control of spectral properties. For example, they can be controlled to
reflect infrared energy during the summer but transmit this energy into the building during the heating
season. Predicted HVAC energy savings for office buildings in arid climates using electrochromic windows
range from 30 to 40 percent.
76
Air Infiltration
The twin goals of reducing energy use while controlling moisture levels can often be at odds. For
example, a reduction in the infiltration of air into a building may also reduce a significant drying mecha 
nism. Adding insulation inside a wall changes the temperature profile within the wall, and so could create
pockets of condensation that would not occur in a less energy efficient wall. Faced with a choice between
a less efficient but sound structure and a more efficient but rotting one, building managers will likely
choose the former. However, current research efforts are expected to identify which structural combina 
tions are more likely to be more successful in different climates, thus removing this barrier to more
efficient buildings.
77
+
Thermal Storage
One way to reduce energy consumption is to increase the thermal storage of the structure,
especially in climates where daily temperature swings require both heating and cooling in the same 
24 hour period. Massive construction materials, such as stone or adobe, have long been used for this
purpose. However, lighter weight thermal storage would be more attractive to consumers. In the near
term, phase change materials (PCMs), including water, salts, and organic polymers, can be used for
thermal storage. In the long term, new solid solid PCMs based on molecular design or nanocomposite
materials may expand the opportunities for building integrated thermal storage.
78
Ideally, such materials
+
will be incorporated as an integral element of existing building components. Annual heating and cooling
savings estimates for simple residential buildings with PCM wallboard range from 15 to 20 percent.
79
Insulation
Vacuum insulation, while more expensive than other insulation products, offers 5 to 10 times the
R value for a given thickness of conventional insulation (Figure 8). It is therefore most likely to be used
28
+
Towards a Climate Friendly  
Built Environment
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